Serial Data Transfer from Arduino to Python

This post is an extension to Structures, Serialisation, XOR Checksums etc. thread.

The code published below is tested boilerplate code for serial transfer of data in the form of structs, from an Arduino to Python.

My thanks to both @frogandtoad and @ZeFerby for their tips and pointers.

An explanation: The values from sensors are gathered and stored in the Arduino in a pre-defined struct object and subsequently sent to Python as a data packet. This data packet is unwrapped by Python into a tuple (an array that can handle different data-types) for further processing.

It should be noted that to resolve any data misalignment the largest data-types are sent first with the smaller data types following in order of size (float = 4 bytes, int = 2 bytes, char = 1 byte).

First the Arduino sketch;

// to maintain data alignment the members of the struct object
// are ordered largest to smallest data type i.e. float = 4 bytes
// uint8_t = 1 byte

typedef struct{
  float afloat = -15.4; // 4 bytes
  uint8_t abyte = 12; // 1 byte
  uint8_t bbyte = 5; // 1 byte
  }data;

data myData; 


void setup() {
  Serial.begin(115200);

}

void loop() { 

  delay(5000);
  Serial.write((const byte*)&myData, sizeof(myData));

}

And now the cleaned up Python sketch:

import serial
import struct

my_comm_port = '/dev/cu.wchusbserial1460'; # *nix comm port notation

try:

    # Change the baud rate here if different than 115200
    ser = serial.Serial(
    port='/dev/cu.wchusbserial1460',\
    baudrate=115200,\
    parity=serial.PARITY_NONE,\
    stopbits=serial.STOPBITS_ONE,\
    bytesize=serial.EIGHTBITS,\
    timeout=None
    )

    print("connected to: " + ser.portstr)

except IOError:

    print("Invalid comm port!")
    exit(1)

# f = float, B = unsigned Char (uint8_t equivalent)

size = struct.calcsize('fBB')
print(size)

def main():

    while True:

        data = ser.read(size)

        #struct.unpack(format, bytestring)
        tup = struct.unpack('fBB', data)
        print(tup[0])
        print(tup[1])
        print(tup[2])

ser.close()

if __name__ == '__main__':
    main ()

Have fun using this in your projects!